1. Field of the Invention
This invention relates to a valve-moving apparatus for an internal combustion engine for controlling operation of an intake valve and an exhaust valve disposed in an automobile engine and the like.
2. Description of the Prior Art
In general, in open/close control of an intake valve and an exhaust valve of an automobile engine, the open/close timing is set according to the operating condition determined from an engine rotation speed, the amount of depression of accelerator pedal, and the like. In such a valve-moving apparatus, there is proposed one which varies a cam profile according to the operation condition to improve the fuel consumption at a low speed and to improve volumetric efficiency into the cylinders at a high speed. This is achieved by varying the open/close timing, lift amount, release time, and the like of the intake and exhaust valves at a low or a high speed.
Specifically, the automobile engine is provided with a high-speed cam and a low-speed cam, the high-speed cam having a cam profile which is able to obtain a valve open/close timing for high-speed operation, and on the other hand, the low-speed cam having a cam profile which is able to obtain a valve open/close timing for low-speed operation. During operation of the engine, the high-speed cam or the low-speed cam can be selectively used according to the operating condition in order to obtain an optimum open/close timing of the intake and exhaust valves.
Further, in such an automobile engine, there has been previously proposed a cylinder-closing mechanism which stops operation of two of four cylinders of a 4-cylinder engine to improve the fuel consumption. That is, in the valve-moving apparatus, during idle operation or low-load operation, the piston operates but operation of the intake and exhaust valves is stopped to discontinue supply of fuel.
This cylinder-closing mechanism for stopping operation of the intake and exhaust valves is generally operated by providing a change-over mechanism in the rocker arm and hydraulically controlling the change-over mechanism. In this case, hydraulic pressure is supplied from a main oil pump of the engine to the change-over mechanism through an oil passage. As shown in FIG. 58, in order to operate the change-over mechanism, there is a necessary minimum change-over requirement hydraulic pressure. However, the hydraulic pressure from a main oil pump of the engine tends to be lower than the change-over requirement hydraulic pressure. Therefore, an assist oil pump is provided in addition to the main oil pump of the engine to obtain a hydraulic pressure for the change-over mechanism higher than the operation requirement hydraulic pressure.
FIG. 59 shows a plan view of a cylinder head showing the valve-moving apparatus having a prior art cylinder-closing mechanism, and FIG. 60 shows a hydraulic passage of the valve-moving apparatus.
As shown in FIG. 59 and FIG. 60, a cam shaft 1202 is rotatably mounted at the center of a cylinder head 1201, and a cam (not shown) is integrally formed at a predetermined position. A pair of rocker shafts 1203 are also rotatably mounted on the cylinder head 1201, parallel to the cam shaft 1202. Bases of a rocker arm 1204 and a rocker arm 1206 having a change-over mechanism 1205 are individually mounted to the rocker shafts 1203, and rocking ends of the rocker arms 1204 and 1206 oppose top ends of intake or exhaust valves 1207. Furthermore, an assist oil pump 1208, an accumulator 1209, and an oil control valve 1210 are mounted on an end portion of the cylinder head 1201. The assist oil pump 1208 can be driven by a driving cam 1211 attached to one end of the cam shaft 1202, and the oil control valve 1210 can be operated by a control signal from a control unit 1212.
When the cam shaft 1202 rotates, the rocker arm 1202 and the rocker arm 1206 are rocked by the cam to drive the intake and exhaust valves 1207. During idle operation or low-load operation, the engine is operated with two of the four cylinders unworked. Specifically, the oil pump 1208 is driven by the driving cam 1211 of the cam shaft 1202, and hydraulic pressure is stored in the accumulator 1209. On the other hand, the control unit 1212 determines the operating condition of the engine from signals from various sensors and sends a control signal to the control valve 1210 to change it over. Then, hydraulic pressure is sent to the change-over mechanism 1205 of the rocker arm 1206 to stop the driving of the corresponding intake and exhaust valves 1207. Therefore, the engine is operated only with the driving of the intake and exhaust valves 1207 corresponding to the rocker arm 1204.